The World Bank has warned of a rocky road ahead for emerging economies, as the US moves to tighten its monetary policy.

But the big development bank’s chief economist also says the US Federal Reserve should hold back on any rate rises until next year to help the slow-growing global economy.

In an update this week, the World Bank cut its forecast for 2015 to 2.8 per cent, slightly lower than the 3 per cent expansion predicted earlier this year.

The downgrade is partly due to contraction in they US in the first quarter, combined with slow turnarounds in Europe, and deceleration in Japan and China.

But the dim view suggests it will be harder for emerging and poor economies in coming months, as many struggle with low commodity prices and capital outflows.

The World Bank report says dropping oil prices oil prices mean lower costs for net energy importers, but because of the stronger US dollar the benefits of cheaper oil are not having a big impact on struggling economies.

The bank warns that such challenges could get worse, as the US economy rebounds and the Fed looks at lifting interest rates.

This will cause more volatility in global markets and suffering in weaker economies.

If the Fed lifts it interest rates, weaker economies will pay more to borrow and find it harder to attract investment, adding even more downward pressure to already-falling currencies.

World Bank economist Kaushik Basu says the the International Monetary Fund is right in saying the US and global economy would be better off if the Fed maintain its rate near zero per cent until early 2016.

Beyond 2015, the World Bank has maintained its forecast for 3.3 per cent world growth.

This year though, the forecast for the United States has been cut by a half-percentage point to 2 per cent.

The outlook the Euro is down to 1.5 per cent, trimmed Japan to 1.1 per cent and China stays stable at 7.1 per cent.

The South Asia region is expected to see 7.1 per cent growth, after a 1 percentage point upgrade in the outlook.

The forecast for developing countries as a whole was cut by 0.4 percentage points to 4.4 per cent.

“Unless emerging markets have taken the prudent policy steps to be fiscally and externally resilient, they may face significant challenges dealing with the turbulence and other fallout that could be associated with a Fed tightening,” added Ayhan Kose, the World Bank's director of development prospects.